The attorney general is likely to lose the right to play a part in prosecution decisions but keep the job of government legal adviser in a shakeup of the role to restore public confidence, the Guardian has learned. The change will form part of Gordon Brown's new constitutional settlement, along with other measures to increase public accountability which opened for consultation last week, including a bigger role for MPs in deciding whether to wage war.

The consultation on the role of the attorney was launched in July and will not conclude until the end of November, but Whitehall sources have told the Guardian that the likely outcome is that, for the great bulk of criminal offences, decisions by the director of public prosecutions would be final. That would mean the attorney would play no role in cases such as the cash for honours investigation. But for a limited number of prosecutions involving the public interest - such as the BAE Systems case - the attorney could retain a function.

Critics claim the attorney's current responsibilities - as legal adviser to government, independent guardian of the public interest, and minister responsible for prosecutions - are fraught with conflicts of interest. Some say a member of the government cannot be trusted to give independent and impartial advice and the job of adviser should be handed over to an outsider or an official.

The inbuilt tensions were highlighted during Lord Goldsmith's tenure when controversy erupted over his advice on the legality of the Iraq war, his insistence on having a say on whether to prosecute Downing Street aides over the cash for honours affair, and his part in the decision to drop a bribery investigation against BAE Systems.

Under the proposed shakeup the attorney would lose any power to direct the DPP to prosecute or not, except possibly for a small number of cases involving national security or the threat of severe damage to international relations. Retaining this exception would be controversial because it would still allow the attorney to interfere in a future BAE Systems scenario.

There is also a small category of cases for which the attorney general's formal consent is required before a prosecution can go ahead. This requirement is likely to be dropped, with the possible exception of Official Secrets Act prosecutions.

Last July the constitutional affairs select committee concluded that the current role of the attorney was "not sustainable" and must be reformed.

The MPs said a conflict between the political and legal aspects of the role had been exposed by the cash for honours inquiry and the decision to drop the Serious Fraud Office investigation into allegations of secret arms deal payments by BAE Systems to Saudi officials.

Lord Goldsmith stepped down when Tony Blair left office. His successor, Lady Scotland, has ruled herself out of any part in prosecution decisions, except where statute requires her consent, pending a decision on reform.

The current thinking in government is that the attorney should not be stripped of the role of legal adviser to the government. "I don't think that's where we will end up," a Whitehall source said. "There is something you will lose by having somebody who is not a ministerial equal. Ministers turn to the attorney general because it's a colleague and they will take hard messages from their equals."

The source said ministers came to the attorney "because they know they will get politically aware advice". If the attorney were to retain a role in an exceptional class of prosecutions, this should be made more transparent, the source said.

The changes are expected to be incorporated in a constitutional reform bill published for pre-legislative scrutiny in the new year.